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The LIGA-technology
At the beginning of micro system technologies "MST"silicon was the preferably used material. Meanwhile metals and metal alloys with adjustable properties are recommended. For functional micro systems surface coatings with improved properties, e.g. hardness or corrosion resistance, are important as well as 3-dimensional micro-components made from metallic materials.
One of the most important operation procedure in micro system technology is the so-called LIGA-technique, consisting a process management of generating a mold using lithography, filling of the mold with metal by electro forming and subsequent replication in plastics by e.g. injection molding or hot embossing.
With the lithographic process step a complex geometric shape can be transferred into a radiation-sensitive polymer (the resist) either by using UV-, X-ray, electron or particle irradiation or direct ablation by e.g. laser techniques.
Besides classical precision engineering diamond cutting or spark erosion techniques are applicable. In addition, using silicon structured by related thin film technologies is possible.
The mold, fabricated by one or by a combination of techniques mentioned above, can be filled with a metal by an electro forming process directly if it is deposited on an electrically conductive material. Otherwise, an additional metallization step of the whole mold is necessary. After the separation from the mold, a metal microstructure can be obtained. These metal microstructure can be the final product or, in some cases, a mold insert for further replication processes like injection molding, hot embossing or a tool for spark erosion techniques. This allows a mass fabrication of microstructures e.g., in plastics or ceramics.
For the fabrication of mold inserts deposited nickel or copper electrolytic deposited from special designed electrolytes are commonly used. Recent developments showing several advantages of electro deposited metal alloys. In particular, nickel iron alloys with different nickel to iron ratios have remarkable higher hardness and corrosion resistance compared to nickel.
Gold electroplating techniques are also used for the fabrication of X-ray masks and gold bumps for flip-chip bonding as well. These are processes with an extremely high request on precision and accuracy.
In most of all cases functional micro systems are not monoliths, but they are assembled from metals, plastics, ceramics or glass. This requires the application of different fabrication technologies at the same time. Some of these, electroplating and wet chemical processing are covered by our equipment, the µGalv and µChem series of the M-O-T Semicon.
